In the meantime, preheat the oven to 400 F. In a saute pan, heat a little bit of olive oil over medium heat. Add in the mushrooms, salt and pepper. Cook mushrooms for about 5 minutes or until slightly brown. Set aside. In a large casserole dish, toss together the cooked ziti, marinara, chicken sausage, mushrooms, ricotta cheese and some salt and pepper. Spread out in an even layer and top with slices of provolone cheese. Cover with foil and bake for 20 minutes. Remove foil and bake 5-6 minutes more.